It is often difficult to sterilize biologically active compounds since the chemical, physical or physiological properties of active compounds are often significantly altered by variations in the compounds surrounding environment. For example, changes in pH, ionic strength, or temperature can result in reversible or irreversible changes in the character of compounds.
Radiation sterilization has the advantages of high penetrating ability, relatively low chemical reactivity, and instantaneous effects without the need to control temperature, pressure, vacuum, or humidity. Radiation sterilization is widely used in industry for a variety of products and both dosage levels and its biological effects are well known. It is generally agreed that electron-beam and gamma sterilization are equally effective in killing microbial organisms. While sufficient to effectively kill microorganisms, the radiation generally alters the structure of proteins, DNA, RNA, etc. as to render it biologically inactive. Therefore there remains a significant need for a simple way to effectively and safely sterilize biologically active compounds without deleteriously affecting their chemical, physical, or physiological properties.
Most injectable collagen materials for human use are prepared by an aseptic process and cannot be submitted to terminal sterilization. Accordingly, they may contain unwanted and potentially dangerous biological contaminants or pathogens, such as viruses, bacteria (including inter- and intracellular bacteria, such as mycoplasmas, ureaplasmas, nanobacteria, chlamydia, rickettsias), yeasts, molds, fungi, single or multicellular parasites, and/or similar agents which, alone or in combination may cause adverse reactions. Consequently, it is of utmost importance that any biological contaminant in the injectable collagen material be inactivated before the product is used. This is especially critical when the material is to be administered directly to a patient.
Most procedures for producing injectable collagen materials have involved methods that screen or test the starting materials for one or more particular biological contaminants or pathogens. Materials that test positive for a biological contaminant or pathogen are discarded. Examples of screening procedures include the testing for a particular virus in the starting material such as human placenta. Then the manufacturing process must include steps for removal or inactivation of the contaminant(s) and/or pathogen(s) from the initial raw material.
Most injectable collagen products on the market are made from a material which is initially sterilized by means such as by filtration of an initial collagen solution, then is processed totally under sterile conditions. A sterility assurance level (SAL) of 10−6 SAL is very difficult to achieve using this process. Results with gamma ray or e-beam irradiation are much better, but the collagen material is frequently damaged using these methods.
In view of the difficulties discussed above, there remains a need for methods of terminal sterilizing injectable collagen material without an adverse effect on the material's desirable attributes.
It is therefore an object of the present invention to provide methods of sterilizing injectable collagen material by reducing the level of active biological contaminants or pathogens without adversely affecting the material.